Sparse, brittle, sulphur-deficient hair is an excellent marker for several autosomal recessive neurocutaneous syndromes. The term 'trichothiodystrophy' is commonly used in publications on such syndromes and the best characterized trichothiodystrophy syndrome is associated with skin photosensitivity and intellectual impairment. Patients with these three cardinal signs usually have an underlying DNA repair defect. Here we describe clinical and laboratory findings in two patients with trichothiodystrophy and defective DNA repair alongside findings in three other cases who have different trichothiodystrophy syndromes without defective DNA repair. These patients' features are discussed in the light of a practical classification scheme which is based upon a check-list of clinical abnormalities associated with trichothiodystrophy syndromes (Van Neste, 1991).